The present invention relates to wireless integrated circuits, specifically to tuned RF amplifiers.
We are presently in the midst of a wireless revolution. Mobile phones, once a novelty referred to as car phones, have become ubiquitous. Wireless personal data assistants, local and wide area networks, and computer connections are now everyday pieces of business equipment. Data and voice telecommunications have changed the structure of the economy, and have changed the way people live their lives. And now, a host of new products, enabled by the Bluetooth standard, are poised to enter a marketplace driven by the promise of a wireless Internet. The present invention provides important improvements to a key circuit used in wireless systems.
This circuit is a tuned RF amplifier. These amplifiers are useful in buffering and providing gain for oscillator, received, and transmit signals in RF integrated circuits.
Wireless devices typically transmit and receive data through the air on high frequency electromagnetic waveforms, though some systems, such as satellite dishes and pagers simply receive, and others merely transmit. Data transmission is begun by encoding the data to be transmitted. In Bluetooth systems, encoded data typically has a rate of 1.5 MHz and is used to modulate a high frequency electromagnetic carrier signal. This carrier signal is in the 2.44 GHz range. The modulated carrier signal is then applied to an antenna for broadcasting. The broadcast signal is referred to as a radio frequency (RF) signal. Data reception involves receiving the RF signal. The signal is then amplified, demodulated, filtered, and decoded.
RF integrated circuits often include a voltage controlled oscillator on-chip. The oscillator generates a local oscillator signal, which is buffered by an RF buffer amplifier and applied to a polyphase filter. Quadrature output signals are provided to receive and transmit mixers. The polyphase filters have a loss of 6 dB from input to output and have a minimum phase error when they receive a sinusoidal input.
Thus, what is needed is an RF buffer amplifier that can provide gain to compensate for the 6 dB loss, provide a sinusoidal output, and do so with a low power supply current. Such a buffer is useful for this, as well as several other functions in an RF integrated circuit.
Accordingly, embodiments of the present invention provide a power efficient RF buffer amplifier that filters signals and produces a large output swing. Specifically, p-channel loads provide a current xe2x80x9cre-usexe2x80x9d path, thereby reducing supply current by approximately half. These p-channel loads are connected in a positive feedback configuration to improve circuit gain and AC performance. The input devices are biased near cutoff, such that only one device conducts at a time, which further reduces supply current.
An exemplary embodiment of the present invention provides a method of buffering RF signals, including receiving an input signal, wherein the input signal alternates between a first polarity and a second polarity. From the input signal, a first current is generated, wherein the first current is proportional to the input signal when the input signal has the first polarity, and approximately equal to zero when the input signal has the second polarity, and a second current is generated, wherein the second current is proportional to the input signal when the input signal has the second polarity, and approximately equal to zero when the input signal has the first polarity. A third current is generated proportional to the first current, and a fourth current is generated proportional to the second current. The first and fourth currents are applied to a first terminal of an inductor, and the second and third currents are applied to a second terminal of the inductor.
A further embodiment of the present invention provides a circuit for buffering RF signals. The circuit includes a first switch coupled between a first supply node and a first output node, a second switch coupled between the first supply node and a second output node, a third switch coupled between the first output node and a second supply node, a fourth switch coupled between the second node and the second supply node, and an inductor coupled between the first output node and the second output node.
Yet a further exemplary embodiment of the present invention provides a circuit for buffering RF signals. The circuit includes a first device coupled between a first output node and a first supply node, where the first device has a control electrode coupled to a first input node and a second device coupled between a second output node and the first supply node, where the second device has a control electrode coupled to a second input node. Also included are a third device coupled between a second supply node and the first output node, where the third device has a control electrode coupled to the second output node, and a fourth device coupled between the second supply node and the second output node, where the fourth device has a control electrode coupled to the first output node. An inductor coupled between the first output node and the second output node is also included.
A better understanding of the nature and advantages of the present invention may be gained with reference to the following detailed description and the accompanying drawings.